1/(2×3)+1/(3×4)+1/(4×5)+1/(5)=1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6=1/2-1/6=1/39.81×1+0.5×98.1+0.04×981=9.81×(1+5+4)=9.81×10=98.1
